1. Field of the Invention
The present invention relates to a wiper system and a wiper control method.
2. Description of Related Art
Rain droplets, which adhere to a front glass of a vehicle (e.g., an automobile), may reduce a visibility of a front view of a driver through the front glass. In order to avoid the reduction in the visibility, a wiper system is provided. In such a wiper system, a wiper is reciprocally swung over the front glass in response to rotation of a wiper motor to wipe the rain droplets adhered to the front glass.
In one such wiper system, the driver of the vehicle may manipulate a wiper switch to change an operational mode of the wiper among multiple operational modes, so that the rotational speed of the wiper motor is changed to change the moving speed of the wiper. The operational modes of the wiper include, for example, a high speed mode and a low speed mode. In the high speed mode, the wiper is reciprocally swung at the high speed. In the low speed mode, the wiper is reciprocally swung at the low speed.
Japanese Unexamined Patent Publication No. 2005-225457A recites a technique, which limits a rapid change in the moving speed of the wiper at the time of changing the operational mode between the high speed mode and the low speed mode. Specifically, Japanese Unexamined Patent Publication No. 2005-225457A recites a wiper system, which includes a link mechanism that converts rotation of a wiper motor in a single rotational direction into reciprocal swing movement of the wiper. When the operational mode is changed from the high speed mode to the low speed mode, the rotational speed of the wiper motor is progressively reduced. In contrast, when the operational mode is changed from the low speed mode to the high speed mode, the rotational speed of the wiper motor is progressively increased.
There is also known another type of wiper system, in which a wiper motor is designed to rotate in a forward direction and a backward direction to reciprocally drive the wiper between an upper return position and a lower return position.
In this type of wiper system, the rotational speed of the wiper motor in the forward or backward rotation of the wiper motor is controlled during the forward or backward swing of the wiper to accelerate, decelerate or stop the wiper. Therefore, when the rotational speed of the wiper motor is changed in response to the operational mode at the time of changing the operational mode, the moving speed of the wiper is rapidly changed. Thus, the smooth change of the operation of the wiper is not possible. For example, when the operational mode is changed from the high speed mode to the low speed mode in the middle of accelerating the moving speed of the wiper, the moving speed of the wiper is temporarily decreased and is then increased once again. Therefore, the wiper looks like being temporarily hitched, so that the driver (user) of the vehicle may have an uncomfortable feeling.